1. Field of the Invention
The present invention relates to a reference supply voltage circuit, and particularly, relates to a reference supply voltage circuit which uses more than two reference supply voltages.
2. Description of the Related Art
There is disclosed in Japanese Patent Laid-Open Publication No. 2001-224169 a semiconductor device for a switching power supply of prior art which reduces electric power consumption to improve power supply efficiency by reducing switching loss during a light load by a simple configuration. A control circuit of the semiconductor device for the switching power supply has an error amplifier for generating an error voltage signal made from a difference between a supplemental supply voltage and a reference voltage, and an element current detecting comparator for comparing an element current detection signal detected by a current detecting circuit with the error voltage signal. Further, the control circuit has a light load detecting circuit which stops outputting a switching signal to a switching device with respect to a switching signal control circuit when the error voltage signal is smaller than a lower limit voltage value, and starts outputting the switching signal with respect to the switching signal control circuit when the error voltage signal is larger than an upper limit voltage value.
However, in the semiconductor device for the switching power supply of the prior art, in the case where a high supply voltage (for example, equal to or higher than 15V) is required, there is such a problem that the circuit size increases and becomes unsuitable for a reduction in size because a plurality of high withstand voltage circuit elements are required. For this problem, there is considered a method which reduces the number of necessary high withstand voltage circuit elements by dividing the circuit configuration into one circuit for operating by a first reference supply voltage and another circuit for operating by a second reference supply voltage which is equal to or lower than the first reference supply voltage. However, in this case, a difference between threshold voltages of the circuit elements in both internal circuits increases, and this may lead to a false operation of the whole circuit.